Field of the Invention
The present invention relates to a compound or a salt thereof, and a contrast agent for optical imaging.
Description of the Related Art
An optical imaging method is known as a method for visualizing information on the inside of a living body in a non-invasive manner. In the optical imaging method, a signal, such as an acoustic wave and fluorescence, emitted from a substance (light absorber) that absorbs light in a specimen in irradiation of the specimen with light is measured for imaging. A technique where a subject is irradiated with light and the fluorescence is measured for imaging is referred to as a fluorescence imaging method. A technique where a subject is irradiated with light and the acoustic wave is measured for imaging is referred to as photoacoustic imaging (hereinafter, sometimes abbreviated as “PAI”).
An organic dye (hereinafter, near-infrared organic dye, alternatively, sometimes simply referred to as “dye”) that absorbs light in a near-infrared wavelength region, such as indocyanine green (hereinafter, sometimes abbreviated as “ICG”), can also be administered to a living body to thereby allow the fluorescence and/or acoustic wave emitted from the organic dye in the living body to be measured. Accordingly, the organic dye such as ICG can be utilized as a contrast agent for optical imaging.
Japanese Patent Application Laid-Open No. 2011-46663 discloses a near-infrared organic dye as a contrast agent for optical imaging, and reports the following: various functional groups are introduced to a methine chain portion of the near-infrared organic dye to result in an improvement in tumor accumulation rate of the near-infrared organic dye.